The present invention relates to a triphenylene derivative useful for a discotic liquid crystal material, an ion-transporting layer structure utilizing a discotxic liquid crystal phase, and an ion-transporting method using the layer structure. The present invention also relates to an electrolyte for use in battery, sensor device, etc., in the field of electronics.
Discotic liquid crystal (phase) is a liquid crystal (phase) discovered in 1977 by Chandrasekhar, et al. (Pramana, 9, 471 (1977)). As described in their paper entitled xe2x80x9cDiscotic Liquid Crystalsxe2x80x9d (Rep. Prog. Phys., 53, 57 (1990)) and in a paper entitled xe2x80x9cDesign and Synthesis of Discotic Liquid Crystal Molecules (in Japanese)xe2x80x9d by Shunsuke Takenaka (Japanese Chemical Society, Seasonal Publication, General Review, vol. 22, pp. 60-), the discotic liquid crystal phase is found in compounds having a disk-shaped core and a plurality of relatively long chains connected to the core. Such compounds may be classified into various types according to their core structure, inclusive of derivatives of hexa-substituted benzene and tri-substituted benzene; derivatives of phthalocyanine and porphyrin; derivatives of triphenylene, truxene and pyrylium, respectively; tribenzocyclononene derivatives, azacrown derivatives, and cyclohexane derivatives.
Based on the structure characteristic of a discotic liquid crystal, several reports have been made suggesting application thereof to devices. A system including conjugated xcfx80-electrons as found in derivatives of phthalocyanine or triphenylene can provide a channel for electrons (or holes) (Piechocki, et al; J. Am. Chem. Soc. 1982, 104, pp. 5245). Further, a system including an annular core as found in an aza-crown derivative, can provide a molecular channel using the central spacing thereof as a selective molecular passage (Lehn, et al.; J. Chem. Soc., Chem. Commun., 1985, pp. 1974).
Compounds having a triphenylene skeleton have been proposed in xe2x80x9cMol. Cryst. Liq. Cryst.xe2x80x9d, 65,307 (1981); xe2x80x9cLiquid Crystalxe2x80x9d, 1986, vol. 1, No. 2. pp. 109-125; Japanese Laid-Open Patent Application (JP-A) 10-120730, etc. However, such compounds per se do not have mesomorphic properties and/or a molecular structure having at least two ether oxygen atoms in their side chains as in the triphenylene derivative according to the present invention specifically described hereinafter.
An ion-transporting mechanism may generally be classified into two types. Specifically, in the case where an electrolyte comprises an electrolytic aqueous solution or an organic electrolytic solution, the ion-transporting mechanism is based on migration of ions dissociated by salvation with a solvent. On the other hand, in the case of an organic solid electrolyte, the ion-transporting mechanism is based on a successive ligand exchange such that ions dissociated by coordination with a polar group (as a donor) are transported by segment movement as in the case of, e.g., polyethylene oxide (PEO). In the former case, an ion-transporting efficiency is higher but its practical application is limited due to the liquid-state transport. In the latter case, the transport mechanism is based on a thermal segment movement of a polymer chain, thus being liable to be affected by a fluctuation in temperature. Further, the polymer chain has a disorderedly entangled structure, thus failing to perform an efficient ion transport.
With respect to polyethylene oxide (PEO), Wright et al. have reported in 1973 an ion conductive characteristic of a complex of PEO with a metal salt and Armand et al. have suggested in 1979 the possibility of use of an electrolyte for a battery. As a result, extensive research and development as to an organic solid electrolyte have been widely made in the world. The solid electrolyte is not in the liquid state, thus being free from leakage thereof to the outside. Further, the solid electrolyte has the advantages of heat-resistance, reliability, safety properties, and size-reduction in a resultant device, when compared with the liquid electrolyte. Further, the organic electrolyte is softer than the inorganic electrolyte, thus being readily shaped or processed advantageously.
Generally, an ionic conductivity of the electrolyte may be represented by a product of carrier density, (electric) charge, and ionic mobility. Accordingly, the electrolyte is required to have a higher polarity for dissociating ions and a lower viscosity for moving the dissociated ions. In view of these properties, the above-mentioned PEO is insufficient to provide the resultant solid electrolyte with such properties. As described above, the ion-transporting mechanism of PEO is based on the successive ligand exchange of dissociated ions by thermal segment movement of its polymer chain, thus being liable to be largely affected by a change in temperature. In order to increase carrier density, when a large amount of metal ion is incorporated in the PEO-based solid electrolyte, crystallization is liable to occur in the system, thus adversely lower the ionic mobility. In order to prevent such a crystallization, derivatives or modified products of PEO insulating one crosslinked with an urethane component (M. Watanabe et al. xe2x80x9cSolid State Ionicsxe2x80x9d, 28-30; 911, 1988), one having a side chain introduced into a crosslinked potion for improving the ionic mobility at low temperature xe2x80x9cPreprints for the 40-th Polymer Discussion (in Japanese)xe2x80x9d, 2766, 1991) and one of fused-salt type having a terminal portion into which a salt is incorporated (K. Ito et al., xe2x80x9cSolid State Ionicsxe2x80x9d, 86-88, 325, 1996 and K. Ito et al., xe2x80x9cElectrochim. Actalxe2x80x9d, 42, 1561, 1977) have been developed.
Such modified PEOs, however, have failed to provide a sufficient ionic conductivity as yet. For this reason, an electrolytic solution comprising a mixture of a high-permittivity organic solvent and a low-viscosity solvent or a gel-type electrolyte wherein an electrolytic solution is solidified by an organic polymeric compound is predominantly used.
Further, in the case of utilizing the solid electrolyte for a battery device, it is important to improve not only the ion-transporting efficiency but also an efficiency of electrochemical reaction.
In view of the above-mentioned problems, an object of the present invention is to provide a triphenylene derivative useful for a discotic liquid crystal material.
Another object of the present invention is to provide an ion-transporting layer structure excellent in ion-transporting efficiency utilizing a discotic liquid crystal phase, and an ion-transporting method using the ion-transporting layer structure.
A further, object of the present invention is to provide an electrolyte, capable of providing a high ion-transporting efficiency and a decreased temperature-dependence of an ionic conductivity, useful for a battery, a sensor device, etc., in the field of electronics.
According to the present invention, there is provided a triphenylene derivative represented by the following formula (I): 
wherein R1-R6 independently denote an ethoxy or propoxy group-containing segment having at least two ether oxygen atoms and a terminal group comprising a linear or branched alkyl group having 1-20 carbon atoms, the alkyl group including at least one hydrogen atom optionally substituted with fluorine atom and at least one methylene group optionally substituted with xe2x80x94Oxe2x80x94, xe2x80x94COxe2x80x94, xe2x80x94CHxe2x95x90CHxe2x80x94, xe2x80x94Cxe2x89xa1Cxe2x80x94 or epoxy group.
According to the present invention, there is also provided an ion-transporting layer structure, comprising:
a plurality of ion-transporting molecules having a polar molecular chain and arranged in a layer wherein a plurality of the polar molecular chains are two-dimensionally extended in a layer direction and associated with each other to form a channel through which an ion is transported in a direction perpendicular to the layer direction.
According to the present invention, there is further provided an electrolyte, comprising: at least one species of a compound comprising a discotic mesogen group and a polar side chain connected to the discotic mesogen group, and at least one species of a metal salt, the electrolyte having a ionic conductivity anisotropy.
These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.